1. Field of the Invention
This invention relates generally to fiber optic detection systems for acoustics and other environmental effects, and more particularly to detection systems that utilize modulation of light signals in optical fibers.
2. Description of the Prior Art
Numerous systems have been developed to take advantage of the phase change undergone by a light beam traversing an optical fiber that is subjected to an acoustical wave. One such system was reported in the article "Single Fiber Interferometric Acoustic Sensor," by J. A. Bucaro and E. F. Carome, Applied Optics, Volume 17, No. 3, pgs. 330-331, Feb. 1, 1978.
In another system described in U.S. Pat. No. 4,193,130 entitled "Fiber Optic Hydrophone" for use as an underwater electro acoustic standard issued to A. Mark Young, et al, a system is proposed that subjects the sensor fiber coil and the reference fiber coil to the same pressure and temperature changes, but separates the reference fiber coil in an acoustically isolated compartment.
In another system described in U.S. Pat. No. 4,238,856 entitled Fiber Optic Acoustic Sensor, issued to Joseph A. Bucaro, light is transmitted into a single mode optical fiber in which optical beams are internally back reflected by the ends of the fiber such that the back reflected beams create a beam excitation having beat oscillations that are detected at the output of the fiber.
Also, U.S. Pat. No. 4,375,680, issued to R. F. Cahill, et al and assigned to the assignee of the instant application describes a fiber optic acoustic sensor based on the Sagnac interferometer.
In all of the systems described it is desirable to provide more accurate systems that minimize extraneous noise offsets that distort the output signal. It is an object of this invention to provide an optical fiber sensor that has a digital output, wide dynamic range, the capability of forming an array out of a single fiber and is compatible with multiplexing techniques allowing arrays to be formed with a single optical processing unit.